To implement the “goods to man” principle, fixed stations for preparing orders generally have a special configuration and must implement several functions, such as for example (without this list being exhaustive):                obtaining supplies two types of loads, namely storage containers (containing products that will be used to prepare the orders) and shipping containers (in which or on which the goods to be shipped will be placed according to the orders);        removing both types of loads, namely storage containers (except in the case of palletization where it is the storage container itself that is placed on the pallet forming the shipping container) and shipping containers (after they have been filled—or loaded in the case of palletization—according to the orders);        synchronization between two different types of flows, one for storage containers and the other for the shipping containers;        accumulating a quantity of loads (i.e. a determined number of storage containers and/or shipping containers) upstream to the operator (or automaton) according to the configuration of the preparing station;        weighing operation performed on one of the two types of loads or on both loads (this weighing function enables the preparing operation to be checked);        classic preparation (the operator picks goods from the storage containers that pass before him and places the picked goods into the shipping containers) and reverse preparation (the operator picks goods from the storage containers that pass before him, the storage containers whose content is thus modified becoming the shipping containers);        exclusion (the possibility of removing a storage container out of an automatic storage depot);        re-procuring supplies of goods (possibility of re-entering a storage container into an automatic storage depot);        inventorying (for example the storage containers are brought out of an automatic storage depot and then made to pass through the preparing station in order to know exactly which goods that contain, and finally they are stowed again in the automatic storage depot);        etc.        
Referring now to FIG. 1, we present a top view of an example of a known configuration for an automated storage system for preparing packages comprising:                a storage depot 7 comprising several (two in this example) assemblies each formed by an alley (or track) 7a, 7a′ serving on either side a storage shelf 7b, 7c, 7b′, 7c′ with several superimposed stowage levels. Each shelf is sub-divided on its length into storage locations, each intended for receiving one container (trays or cardboard boxes for example) for storing goods. At each stowage level, each alley receives paths for moving a trolley (also called a shuttle) which shifts the storage containers and places them inside or removes them from the storage locations. The trolleys can move horizontally at a given stowage level, as well as vertically from one level to another of an alley by elevators each placed at one end of an alley;        a set of conveyors taking the storage containers from the storage depot up to the preparing stations and vice versa. In the example of FIG. 1, three sub-assemblies of conveyors can be distinguished: the first (referenced 9) is placed immediately at the exit from the depot 7 and comprises conveyors placed in the axis of the storage shelves; the second (referenced 16) comprises conveyors placed perpendicularly and after those of the first sub-assembly; the third (referenced 8) comprises conveyors placed perpendicularly and after those of the second sub-assembly, as well as along one of the storage shelves 7b of the depot 7. The running surface height (RSH) of the conveyors used in the sub-assemblies 6, 7 and 8 generally ranges from 750 to 1750 mm;        several (six in this example) order-preparing stations 10a, 10b, 10c, 10d, 10e and 10f each occupied by one operator 1a, 1b, 1c, 1d, 1e and 1f and extending perpendicularly to the conveyors of the above-mentioned third sub-assembly 8. An example of a configuration of a preparing station is described in detail here below;        a central management computer system (not shown) (also called a steering or managing system) responsible for managing the entire automated storage system (storage depot, set of conveyors and preparing stations). It also manages the list of orders associated with each shipping container (packages) and therefore the order of the order lines forming this list according to the location of the storage containers in the storage depot, the availability of the trolleys and elevators of the storage depot as well as requirements in goods for the different shipping containers (packages) to be prepared that succeed one another other at the preparing station. This is aimed at optimizing all the movements and the times of preparation of the shipping containers (packages) and providing for synchronization between the arrival, at the preparing station, of a shipping container (package being prepared) and the storage containers (containing goods indicated in the order list associated with this storage container).        
In one embodiment, each preparing station comprises the following (the references given here below are those of the elements of the station referenced 10a):                a first circuit of conveyors for the storage containers formed by two horizontal columns of conveyors: one (outbound column 2) for moving the storage containers from the third sub-assembly of conveyors 8 to the operator 1a and the other column (return column 3) for the reverse movement; and        a second circuit of conveyors for the shipping containers formed by two horizontal columns of conveyors: one (outbound column 4) for moving the shipping containers from the third sub-assembly of conveyors 8 to the operator 1a, and the other column (return column 5) for the reverse movement.        
In each of the first and second circuits, the outbound columns 2 and 4 (formed by classic horizontal conveyors) perform the function of collecting a determined quantity of containers upstream to the operator (or automaton).
A storage container takes the following route: it is picked up by a trolley in the storage depot 7 then conveyed successively by the conveyors of the first, second and third sub-assemblies 9, 6 and 8 and then by the conveyors of the outbound column 2 and is then presented to the operator. In the other sense (after being presented to the operator), the storage conveyor takes the reverse route: it is conveyed by the conveyors of the return column 3, and then successively by the conveyors of the third, second and first sub-assemblies 9, 6 and 8 and finally placed again in the storage depot 7 by a trolley.
It must be noted that the storage containers must be presented in an order to the operator. The same is the case for the predetermined shipping containers. Furthermore, as already indicated here above, the flow of storage containers must be synchronized with the flow of shipping containers. Typically, for a given shipping container taken before the operator (for example to his left), several storage containers containing goods that he must pick up and place in the given shipping container are made to file past him.
In order to relax constraints at the storage depot, it is accepted that the containers (storage containers or shipping containers) do not exit the storage depot in the order in which they have to be presented to the operator. It is therefore necessary to perform an operation for sequencing the containers between the storage depot and the preparing station in which the operator is situated. In the example of FIG. 1, this sequencing operation is performed by the second sub-assembly of conveyors 6 which itself performs a buffer role: the storage containers circulate therein in a loop and when the storage container expected on the conveyors of the outbound column 2 arrives before this column (in order to make the full complement of the sequence of storage containers awaited at the preparing station), this container is transferred to the conveyors of the outbound column 2, the other storage containers continuing to circulate on the second sub-assembly of conveyors 6. This method is performed for each of the storage containers expected in a predetermined order of arrival at the preparing station.
Classically, this order of arrival is predetermined (i.e. determined for each container before this container reaches the preparing station) by the managing or steering system and, if necessary, recomputed during the routing of the containers from the output of the storage depot to the preparing station in which the operator is situated (for example to take account of a malfunction in an element of the system).
The running surface height (RSH) of the conveyors used in these first and second circuits is generally 750 mm.
In the example illustrated in FIG. 1, the return column for the shipping containers 5 is common to the preparing stations referenced 10a and 10b (these two adjacent stations are configured symmetrically relative to each other, the common column forming an axis of symmetry). This is also the case for the adjacent preparing stations referenced 10c and 10d as well as for those referenced 10e and 10f. This reduces the footprint of the preparing stations.
Unfortunately, despite this solution, the current approach based on classic horizontal conveyors (as described here below with reference to FIG. 1) has several drawbacks.
First of all, it consumes an excessive amount of m2 for a small running surface height (750 mm typically). As an example of this excessive footprint, the surface area needed for six order-preparing stations (as in the example of FIG. 1) is in the range of 100 m2.
Another drawback is that classic horizontal conveyors in the preparing stations have such density on the ground that it makes it difficult to obtain maintenance access to these conveyors (the conveyor area is far too dense).
Another drawback is that, without even further increasing the footprint of the preparing station (by increasing the length of the outbound column of each of the first and second circuits), it is not possible to increase the number of containers that can accumulate upstream from the operator (or automaton).
Yet another drawback is that, in certain configurations, the footprint of the preparing stations prevents or makes it difficult to obtain maintenance access to the trolleys (also called shuttles) used in the storage depot. The maintenance of these trolleys then sometimes makes it necessary to access the storage depot from the rear with a girder system (referenced 11 in FIG. 1) which is not ergonomic.
Yet another drawback is that it is not possible to obtain optimal processing when one and the same container has to be presented to the operator several times in succession. For example, for two distinct orders, the operator must pick an item from a given storage container and place it in a first shipping container and then, a few moments later (and after one or more other storage containers have been presented to him), the operator must pick another item from the same given storage container and place it in a second shipping container. Indeed, going back to this same example, currently, the second sub-assembly of conveyors 6 is used for an operation to introduce the given storage container into the outbound column 2 of the first circuit of the preparing station (10a for example). This is not optimal because the time interval between two successive presentations of the same container to the operator cannot be small: it is the time taken by this container to travel throughout the next circuit: i.e. it has to travel through the conveyors of the return column 3, then the conveyors of the second sub-assembly of conveyors 6 and finally the conveyors of the outbound column 2. In practice, if this time interval is too great, then two storage containers containing the same type of goods required for the two orders involved are made to exit the storage depot. The number of motions performed by the storage depot is thus increased, which is not a satisfactory solution. Moreover, to manage this increase in the number of motions performed by the storage depot, the number of alleys of the storage depot is generally increased (so as not to exceed a maximum capacity of entries/exits that can be made by the elevator or elevators placed at each end of an alley).